Service brakes and safety catch devices are absolutely necessary in elevators, which service brakes and safety catch devices reliably decelerate the car of the elevator to a standstill in the case of excessive speed and/or uncontrolled travel movements.
Service brakes of this type can act, for example, on a traction sheave of the elevator or can be arranged on the car of the elevator and can act on the guide rails.
A brake device preferably produces a constant brake force which is usually set in such a way that the car which is loaded with a nominal load is braked with a deceleration of from 0.8 to 1 g for safety catch devices and from 0.3 to 0.5 g for service brakes.
In order to minimize the risk of injury to elevator passengers during a brake operation of the car, the brake deceleration of the brake device can be limited by way of setting, for example by way of controlling or regulating. Since the brake deceleration of the car is dependent on the car weight and the loading of the car, the brake force should be adapted to the loading of the car. With increasing complexity, a brake device of this type still has to ensure the required degree of safety. It is one safety requirement that the brake device operates according to the closed circuit principle (active when switched on). However, the closed circuit principle requires a continuous feed of energy into an actuator system of the brake device. This leads to an increased energy consumption of the brake device.
If, in contrast, the brake device operates according to the open circuit principle, an energy store is required which provides the energy which is required for closing the brake device if an energy supply of the brake device is interrupted. Since a regulation of the brake force is associated with a high energy requirement, great energy quantities have to be provided. This leads to a brake device with a complex construction.
The brake lining, in particular the coefficient of friction between the brake lining and the guide rail or the traction sheave, has a further decisive influence on the brake force. A change in the coefficient of friction has a direct action on the brake force and on the deceleration which is set. If a brake force correction upon a change in the coefficient of friction is not provided, this has the consequence that the brake force either increases and the car is decelerated to a more pronounced effect, or else the brake force decreases if, for example, oil is situated on the guide rail and the car then cannot come to a standstill.
Furthermore, brake devices, in particular brake linings which are frequently used in a service brake, are subject to wear.
A brake device on the car can comprise two brake units which act in each case on one of two guide rails. The two brake units of the brake device are connected rigidly (positively) to one another via a shaft. This has the consequence that first of all the same brake forces act on guide rails which are arranged on the two sides of the car. As a result of tolerances, guide rail condition or different contamination, however, different brake forces can act on the two sides of the car on account of the abovementioned wear processes and can additionally load the car by way of a torque which is set as a result.
EP 2 058 262 B1 has disclosed a brake device for braking a car of an elevator system, which comprises a pawl which can be adjusted between two operating positions. In the first operating position, the pawl is connected to a brake module in such a way that a release force is transmitted from the pawl to the brake module. In the first operating position, the width of the air gap between the brake module and the device can be set by way of regulation of the release force, in order to set the brake force in this way. In the second operating position, an emergency brake operation of the car takes place, by the pawl being disconnected from the brake module.
There is a need for an elevator with a brake device, the brake device providing a brake force of a magnitude which can be set and is therefore adapted to the respective operating situation, and which brake device has a simple construction.